Calender

ABSTRACT

The invention concerns a calender which comprises a vertical stack of interlinked rollers driven individually by regulated electric motors. The regulation process acts on the distribution of the delivered power to the individual rollers such that the forces acting on the rollers in the horizontal direction and measured in the roller bearings are minimized, so enabling slimmer rollers to be used.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.11/328,545 (Attorney Docket No. 081230-000300US), filed Jan. 9, 2006,which was a continuation-in-part of, and claims the benefit of priorityfrom U.S. application Ser. No. 10/686,024 (Attorney Docket No.081230-000200US), filed Oct. 14, 2003, which was a continuation-in-partof U.S. application Ser. No. 09/604,837 (Attorney Docket No.081230-000100US), filed Jun. 27, 2000 (now U.S. Pat. No. 6,666,135);which was a continuation-in-part of U.S. application Ser. No. 09/117,753(Attorney Docket No. 081230-000000US), filed on Mar. 22, 1999 (now U.S.Pat. No. 6,095,039), which was a 35 USC §371 filing of PCT/EP97/06474,filed Nov. 20, 1997, which is a European PCT filing of GermanApplication No. 196 50 576.3, filed Dec. 6, 1996, the full disclosuresof which are incorporated herein by reference.

BACKGROUND AND SUMMARY OF THE INVENTION

The invention relates to a calender for treating a product web, inparticular a paper web, for example a smoothing calender.

A calender of this type is disclosed, for example, by DE-U-295 04 034.In this calender, an intermediate roll in the roll stack is usuallydriven and drives the other rolls along by means of friction with theproduct web. In the document cited, it is specified that the normallypassively driven rolls are driven actively in order to thread theproduct web into the nips. This auxiliary drive needs to be designedonly for the idling power until the operating speed is reached, whereasthe main drive has to be designed for total power output duringoperation.

Forces that are fed in from the outside act on the rolls in the verticaldirection, as does the weight, increasing from top to bottom, of therolls mounted above. Deformations that are caused by this—in particulardeflection—can be compensated for by means of the deflection controlledrolls. However, forces act on the rolls in the horizontal direction aswell. These forces can be attributed to the friction-induced torquetransmission mentioned, as is explained in the publication Pav/Svenka,“Der Kompaktkalander—die Antwort auf die Herausforderung nach hohenGeschwindigkeiten bei der Glattung und Satinage” [The compactcalender—the answer to the challenge of higher speeds in smoothing andcalendering], DAS PAPIER 1985, pp. V178 ff. In this publication, mentionis also made of a compact calender, in which four resilient rolls withtheir own drives form nips around a hard base roll that is mounted in astationary manner. This is intended to dispense with the interlinking ofthe roll set, as is unavoidable in the case of calenders of this type.

Whereas vertical deformations of the rolls, as explained above, can becompensated for, this does not apply to deformations resulting fromhorizontally acting forces. This means that the rolls must have minimumdiameters in order that horizontal deformations can be kept withintolerable limits. One of these limitations resides in the fact that, inthe event of a deformation of a roll in the horizontal direction, thedistribution of the line load becomes non-uniform, the regions close tothe bearings being loaded more severely. This can lead to over-pressingof the product web in the edge region and to the unequal distribution ofthe product-web property values in the cross-machine profile.Furthermore, increased wear of the resilient roll covers and, in theextreme case, destruction of the same can occur. At a given line load,the compressive stress is limited by the minimum diameters of the rollsto an appropriate value, which may be increased only by increasing theline load. However, even if the horizontal deformation of the rolls iskept within limits, shear stresses nevertheless act on the product webin the nip and--in the case of paper—can loosen the bonding between thefibres in the web running direction and thereby reduce the strength ofthe paper.

The object of the invention is to provide a calender which is costeffective in construction and operation.

A calender according to the present invention minimizes treating defectsin the product web.

The drives apply the specific power for the respectively driven roll,this power being composed of re-forming, transporting and loss power. Inthis case, a distribution of 50:50 to the two nip-forming rolls would beonly a rough guide, since, for example, a deflection controlled roll hasconsiderably higher friction losses than a normal solid roll.

The forces which are to be controlled out according to the invention canbe measured, for example, in the roll bearings; bearings withforce-measuring systems incorporated are commercially available.However, it is at least also conceivable to use measurement methods toregister the horizontal deformations that are brought about by suchforces.

Preferred embodiments of a calender according to the invention areillustrated in the appended drawings and will be explained below indetail.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a largely schematic side view of a calender according to theinvention.

FIG. 2 shows a second embodiment in a similar illustration

FIG. 3 shows a modification of the second embodiment.

FIG. 4 is a block diagram of the control of one of the rolls.

FIG. 5 shows a schematic side view of a third exemplary embodiment of acalender according to the invention.

FIG. 6 shows a schematic side view of a fourth exemplary embodiment of acalender according to the invention.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

A calender frame 10 with side uprights is designed as a welded or castconstruction. Arranged in the frame 10 is a calender 12, which has eightnip-forming rolls. The top and the bottom rolls 14 and 16, respectively,are deflection controlled rolls, and the yoke of the upper deflectioncontrolled roll is clamped immovably in the frame; the bearings of thisroll are also immovable. The roll 14 is provided with a resilient cover,as are the lower deflection controlled roll 16 and the rolls 18, 20 and22, which are provided in the calender 12. Arranged between the rolls 14and 18 is a hard, heatable roll 24, which forms a nip in each case withthe rolls 14 and 18 respectively arranged above and below it. Inaddition, between the rolls 18 and 20 there is a hard, heatable roll 26,which defines a nip with each of these rolls. The nip through which theproduct web 28 passes between the rolls 20 and 22 is used not only forre-forming the product web but also as a reversing nip, in order to turnthat side of the product web that previously faced the resilient rollstowards the hard, heatable roll 30, which is arranged between the rolls22 and 16. (The relevant side of the product web has already passedthrough four nips albeit facing a resilient roll in each case, but hasnevertheless been smoothed to such an extent in the process that passagethrough two further nips on the heated side is sufficient).

The bearings of all the rolls, with the exception of the upperdeflection controlled roll 14, are arranged in the frame 10 such thatthey can be displaced by sliding. The loading of the nips is carried outby means of hydraulic cylinders 32 and results, for example, in anaverage line force of 500 N/mm. It should be noted that the line forcecan also be applied by means of the deflection controlled rolls. Thehard rolls may be heated with steam to, for example, up to 200.degree.C. The resilient rolls may be temperature-controlled. The product web 28is led between the individual nips around guide rolls 34, whose surfacesare provided with spiral grooves in order to ensure that the product webis kept spread out and to prevent the formation of an air cushion onwhich the product web could float. Pneumatic compensation of theoverhanging loads is carried out by means of compensation units 46, inwhose stead hydraulic or other servo drives may also be provided.

Normal spreader rolls may also be provided. The calender arrangementshown can be arranged downstream of a paper or coating machine as an“in-line calender”, or can operate as an “off-line calender”.

The arrangement described thus far largely corresponds to the prior art,apart from the fact that the diameter of the rolls between thedeflection controlled rolls, but at least of the hard rolls, isconsiderably smaller than usual.

According to the first variant of the invention, each nip-forming rollis provided with its own drive, comprising an electric motor, forexample a DC motor, which is coupled via a cardan-shaft to the rollassigned to it and which is fed from a regulated supply unit. In FIG. 1,the drives are indicated only by the usual two-quadrant circle symbol.

FIG. 4 shows the drive to one of the rolls. The drive motor is a DCmotor 50, fed from a converter 52 via a controller 54, preferably adigital PID controller.

In the start-up phase, the rotational speed of each motor 50 is measuredand controlled. An actual-value transmitter in the form, for example, ofa tachogenerator 56; the set points can be stored in an electronicmemory 58, which is read out sequentially. In the start-up phase, theset points are selected such that the rolls which in each case define anip have the same circumferential speed.

In the operating phase, the circumferential speed is a suitableparameter only to a limited extent, since the resilient rolls certainlydeform in the region of the nip, that is to say there is no longerstrict proportionality between rotational speed and circumferentialspeed. This is correspondingly true for the expansion which occurs whena roll is heated.

To overcome this limitation, instead of detecting circumferential of therotational speed, the torque of each drive is detected by torquedetecting devices 66. The torque detecting device 66 is included in anelectronic control system of each motor 50, as indicated in FIG. 4. Atorque detecting device 66 electronically determines the amount of powera motor 50 consumes.

Power control is carried out during the operating phase. Each roll issupplied with an amount of power which, at least approximately, covershalf the re-forming and transporting power transmitted to the productweb in each nip defined by the said roll, plus the loss power. It shouldbe noted that the drive power of the guide rolls 44 in the embodimentillustrated is transmitted by means of the product web in the manner ofa flexible gear mechanism; this power therefore also has to be takeninto account when calculating the set points—also stored in the memory58. However, it is preferred, particularly in the case of larger in-linecalenders, to provide the guide rolls with their own drives as well.

The power control arrangement has the special feature that, whenmetering the power to the motors, which each drive pairs of rolls whichbound a nip, the power of both motors is adjusted in the event of aset-point deviation and, since all the rolls are linked to one another,this means a control intervention in all the motors. An overallcontroller 60 is therefore placed hierarchically above the individualmotor controller and in the event of a set-point deviation, even just inthe case of a single roll, calculates new set points for the power forall the rolls or takes these set points from a look-up table memory.

Arranged in the bearings of the rolls are force sensors, which sense atleast the forces that are transmitted in the horizontal direction fromthe relevant roll to the frame 10. Such “force-measuring bearings” areoffered, for example, by SKF Kugellagerfabriken GmbH, Schweinfurt. Asmentioned above, the power or, more precisely, the power distribution iscontrolled in such a way that these horizontal forces are kept as smallas possible.

The calender arrangement according to FIG. 1 can be operated in such away that the number of nips through which the web passes is predefined;furthermore, the operator is able to influence the technological resultby selecting the line load and the roll temperatures.

FIG. 2 shows, as a second embodiment, a double calender having in eachcase only two nips for calendering one of the product web sides in eachcase. The elements of the calender on the left in the drawing aredesignated using the reference symbols of analogous elements in FIG. 1;in the case of the right-hand calender, an index stroke “'” is added ineach case. It can be seen that each individual calender also has justtwo deflection controlled rolls 40 and 42 with a resilient cover, and ahard, heated roll 44 arranged between them.

FIG. 3 illustrates an example of the second variant of the invention,derived from the embodiment according to FIG. 2. Here, the hard, heated,intermediate roll 45 does not have its own drive, but rather is drivenalong by the covers of the deflection controlled rolls 40, 42. Althoughthe latter transmit the drive torques through the product web to thehard roll 46, the drives of the two resilient rolls are controlled insuch a way that the forces acting on the hard roll are equal andopposite.

It is assumed that, for example in the case of smoothing calenders, theextremely high compressive a stresses in the nips, in combination withhigh temperature, mean that good technological results can be achievedwith the configurations illustrated in FIGS. 2 and 3. In addition tosuch a 3/3 configuration, numerous further configurations in which ineach case a hard roll is arranged between two resilient rolls, such asthe configurations 5/3, 7/3, 5/5, 8/5 and so on, are conceivable.

FIG. 5 shows a fourth exemplary embodiment of a calender according tothe invention, which differs from the first exemplary embodimentillustrated in FIG. 1 in that the loading plane runs in at an anglerather than in the vertical direction. The displacement forces acting atright angles to this inclined loading plane are minimized by theconfiguration according to the invention with individual power drivesand control of the drive power of the latter in such a way that thedrive torques transmitted by the rolls are kept to a minimum. Otherwise,the explanations relating to the first exemplary embodiment apply in acorresponding way here.

The same applies to the exemplary embodiment shown in FIG. 6 of acalender with a loading plane 1 which runs in the horizontal direction,so that the displacement forces acting at right angles thereto actvertically here.

Although the invention has been described in some detail by way ofillustration and example, for purposes of clarity and understanding, itwill be obvious that certain changes and modifications may be practicedwithin the scope of the invention.

1. A calender for treating a product web, said calender comprising: aplurality of rolls arranged along a loading plane in a roll stack havinga first end and a second end, the plurality of rolls including hardrolls, and resilient rolls and treating nips, wherein each treating nipis formed by a juncture of one of said hard rolls and one of saidresilient rolls; an electronic memory for storing set points for astart-up phase and an operating phase of the calender; a power controlarrangement; a plurality of drives, with one drive connected to eachroll in the treating nip; a plurality of transmitters for measuringrotational speed of the rolls, one transmitter being associated to eachdrive respectively; a plurality of torque detecting devices, one torquedetecting device being associated to each drive respectively, configuredto detect a torque of the respective drive; wherein the power controlarrangement is adapted to apply specific power from each drive to itsrespectively driven roll, wherein in the start-up phase the rotationalspeed is controlled by detecting the rotational speed of the rolls bythe transmitters and in the operating phase power control is carried outfor each roll with the power control arrangement by detecting the torqueassociated with the respective roll, wherein the power includesre-forming, transporting and loss power.